Передвижение шарика — QBasic(Бейсик)

CLS
SCREEN 1
x = 150
y = 100
CIRCLE (x, y), 20, 2
DO UNTIL a$ = "q"
    a$ = INKEY$
    IF a$ = "a" THEN GOSUB a:
    IF a$ = "b" THEN GOSUB b:
    IF a$ = "c" THEN GOSUB c:
    IF a$ = "d" THEN GOSUB d:
LOOP
END
a: CIRCLE (x, y), 20, 0: y = y - 5: CIRCLE (x, y), 20, 2: RETURN
b: CIRCLE (x, y), 20, 0: y = y + 5: CIRCLE (x, y), 20, 2: RETURN
c: CIRCLE (x, y), 20, 0: x = x - 5: CIRCLE (x, y), 20, 2: RETURN
d: CIRCLE (x, y), 20, 0: x = x + 5: CIRCLE (x, y), 20, 2: RETURN